Controllable hydraulic pump or motor



Dec. 28, 1965 G. WlGGERMAN N 3,225,699

CONTROLLABLE HYDRAULIC PUMP OR MOTOR Filed Aug. 20, 1962 2 Sheets-Sheet 1 Dec. 28, 1965 v G. WIGGERMANN CONTROLLABLE HYDRAULIC PUMP 0R MOTOR 2 Sheets-Sheet 2 Filed Aug. 20, 1962 United States Patent 9 Claims. (or. 103120) My invention relates to hydraulic positive displacement machines suitable as pumps or motors, and more particularly to hydraulic gear pumps and gear motors in which several gear wheels are situated in a common housing so that they revolve and mesh together continuously.

The invention will "be described herein in terms of a pump, although it is also applicable to the same unit usable as a motor.

Heretofore, in hydraulic machines of this type, in principle, in order to separate hydraulically the inlet flow chamber, which during operation is situated on the disengaging side of the meshing teeth, from the outlet flow channel, situated on the engagement-approaching side of the meshing teeth, it was necessary to have the individual gears fit within the housing with very slight surrounding clearance, not only at the frontal gear wheel surfaces, but also at the outer tooth-head surfaces, i.e. at the outer circumferences of the gears.

In spite of the exacting machining of the housing thus made necessary, gear pumps are relatively inexpensive and, more important, are quite practical and durable. Consequently, there is a tendency to employ gear pumps and gear motors in so-called oil-hydraulic systems. In such systems, because of the predominating tendency towards the lowest possible viscosity and high pressures of the driving medium, even in precision-gear pumps, the internal leakage loss mounts so high that with increased output pressure, the pump output decreases to an inadmissible extent, and furthermore, an undesirably high overheating of the working medium (e.g. oil) takes place.

Known suggestions for improvement, therefore, aim at reducing the above-mentioned internal leakage losses to a practical value. For this purpose it is customarily necessary to adapt the width of the space between the housing and the gears to the prevailing outlet pressure. This can be done, for example, by replacing the two housing walls, situated against the front surfaces of the gears, in a known manner by special axially movable cover members which, by means of certain structural arrangements, are pressed against the gear wheel surfaces by the instantaneous prevailing working pressure itself with such force that only a very slight clearance loss is possible at this point. Unfortunately, to achieve the initial compression, always necessary in connection with gear wheels, the abovementioned movable cover members must have a profile accurately adapted to the figure-of-eight shape of the gear pump housing cross section. Moreover, the cover members must either fit into the pump housing directly with extreme precision, or they must be sealed by means of auxiliary sealing elements, which the complicated profile likewise makes difficult, in such a way that the heretofore required axial movement is permitted. Although the above-mentioned sealing problems at the frontal gear wheel surfaces can be solved in a practical way, the equally necessary improvement in the circumferential sealing of the gear wheels remains an unsolved problem.

It is, therefore, an object of my invention to provide a comprehensive solution of these existing sealing problems.

It is a further object of my invention to provide a hydraulic positive displacement machine which has a "ice minimum of internal leakage loss without the necessity for close dimensional clearance between the pumping gears and contiguous housing portions at the gear peripheries.

To these ends, and according to the invention, the entire gear pump is built on a fundamentally new principle, which, due to a special arrangement of the gears, renders the heretofore necessary circumferential sealing of the gears in the housing quite superfluous. The primary characteristic of the gear pump made in accordance with the invention comprises one or more closed gear trains, each composed of a minimum of four gears, so arranged that the two groups of meshing teeth of each gear correspond to respectively different pitch circle diameters.

If the frontal surfaces of such a gear train are covered by the housing or some equivalent element and the gears are set in motion, depending on the direction of their rotation, the unsymmetrical engagement of the meshing teeth will result in a flow of the medium surrounding the gear train towards or away from the cavity enclosed between the gear train and the frontal cover elements.

A gear pump made in accordance with the invention has the impressive advantage of not requiring any circumferential or tooth-head sealing of the gears, so that, in contrast to previous gear pumps, the housing no longer needs to have a figure-of-eight-shaped recess. A substantial clearance can be provided between the housing and the gears, and the contact surface between the flat parts of the housing and the front faces of the gears can be reduced to a minimum, thus permitting a substantial reduction in friction losses.

According to another, more specific feature of my invention, the advantages of the novel gear pump may be more fully realized in combination with certain principles already known, so that the frontal surfaces of the gears in the gear train are sealed by means of at least one axially movable sealing plate. Due to the absence of circumferential scaling for the gears, the sealing means used in the novel pump can be made much simpler and less expensive than those used in previous gear pumps referred to above. In accordance with the invention, the sealing plate need be made only large enough to cover slightly more than the area of the meshing zones together with the parts of the teeth which project into the space enclosed by the gear train. The sealing plate is so loaded in the direction of the gears by at least one piston-like element, acted upon by the instantaneous prevailing workmg pressure, and supported, for example, on the walls of the housing, that it continuously exerts the slight overpressure needed to insure a tight seal. The elimination of the complicated circumferential seal heretofore necessary, and the ease with which the cylindrical piston or pistons can be manufactured, bring important advantages in production and hence in reduced cost.

According to still other features of my invention, the gears in the gear train of the novel gear pump may be mounted in the housing in such a way that they are fixed in position but free to rotate, or they may be adjustable. The outward effect of such a fixed-position system would correspond to that of previous gear pumps of ordinary design with a given speed and output. According to the last-mentioned feature, at least each alternate gear in the gear train is made capable of radial displacement, so that its two instantaneous pitch circle diameters can be continuously varied in opposite senses. In this manner, the speed and output of the pump can be continuously adjusted from zero to a certain maximum determined by the kinematic characteristics of the toothing. More advantageously, by providing an adjusting device, the invention affords the opportunity of developing the radial displacement of the above-indicated gears to extend beyond their normal center position even as far as the opposite kinematic limit of'the gear system. By means of this structural device, the output of the novel gear pump can be continuously regulated in both directions of flow from a central zero-output position.

The fact that the novel pump can also be used as a gear motor or as a pump and motor alternately needs no special explanation. Moreover, the proposed closed gear train with a minimum of four Wheels is not restricted to a definite kind and size of gear nor to a definite arrangement of such gears. Apart from spur gears, the gear train may consist, for example, of a combination of internally and externally toothed gears, or even of bevel gears. The principle of the closed gear train acting as a displacement machine element, on which the invention is founded, also permits the expansion of the gear train from one with four gear wheels to one with any higher even number of wheels, as well as a suitable combination of gears to form an assembly containing several closed gear trains, permitting either several separate and independently adjustable output flows, or one or several combined adjustable output flows. All gear pumps built on the principle of the invention have the most important characteristic of the invention in common, namely gears that revolve freely in the housing with a substantial clearance at the tooth-head or perimeter.

The foregoing and more specific objects and features of my invention will be described in the following, with reference to the embodiments of controllable and reversible gear pumps according to the invention illustrated by way of example on the accompanying drawings in which:

FIG. 1 is a gear pump according to the invention having four gear wheels, and with the closure plate removed;

FIG. 2 is a vertical section through the same gear pump of FIG. 1;

FIG. 3 is a horizontal section through the same gear pump of FIG. 1;

FIG. 4 is a schematic view of a six-wheel gear pump according to the invention with the gear axes arranged on a circle;

FIG. 5 is a schematic view of a six-wheel gear pump with the gears arranged on the planetary principle.

In all illustrations, functionally similar components are denoted by the same respective reference numerals.

The gear pump illustrated in FIGS. 1-3 has a housing 1 and closure plate 1' in which are mounted a driving gear 2 on a drive shaft 3, and a second gear 4 on a spindle 5. These gears are mounted inside the housing 1 and closure plate 1' in such a way that they are fixed in position but are capable of rotation. Spindle 5 is journaled with an oil-tight fit in corresponding bores in the housing and closure plate 1, 1'. The housing 1 and closure plate 1' are clamped together by a crossbolt 6 and other bolts (not shown) to form a rigid box. The closure plate 1 is provided with a central cylindrical recess 7 for receiving a piston-like extension 8 of a rocker member 8, which member is thereby provided with a radially fixed but axially movable and pivoted mounting in the pump housing. The extension 8' is provided with an annular groove into which a sealing element, for example an O-ring 9, is inserted to insure a tight fit between extension 8' and recess 7. On either side of the centerline of the housing, i.e. of its axis of rotation, the rocker member 8 is fitted with a respective rigidly mounted bearing pin 10, on which respective gear wheels 11 are rotatably supported. Gears 11 permanently engage the other two gears 2 and 4 already mentioned. The rocker member 8 can be pivoted from the outside, for example by means of a lever 12, through an angle [3 on either side of a central position corresponding with the horizontal axis designated by XX in FIG. 1. This movement is communicated to the rocker member 8 through a control shaft 13 which is centrally mounted in the housing 1 and connected with the rocker member by a system of gear teeth. The sides of the housing 1 and rocker member 8 facing towards the gears are virtually flat over an area corresponding roughly to the four tooth-meshing Zones, so that the space 14 enclosed by gears 2, 4 and 11 is substantially sealed off, although it remains hydraulically connected with connecting passage 18 of the housing 1 through the central bore 15 in the rocker member 8 and through axial bores 16 in the toothed disc 17 rigidly connected or integral with the control shaft 13. Otherwise, gears 2, 4 and 11 are separated from the walls of the housing by a substantial clearance, and the cavity 19 thus formed in the housing 1 has a connecting passage 20 leading to the outside.

The mode of operation of the pump according to FIGS. 1-3 is as follows. When the drive shaft 3 is rotated and the control shaft 13, and hence the rocker member 8, are in the neutral center or zero position, the axes of all the gears 2, 4 and both gears 11 will be the same distance apart, and thus the four gears mesh with the same pitch circles of contact. Since at the entry points of closed gear trains having an even number of teeth there are always as many pairs of teeth approaching the enclosed cavity as moving away from it, provided the pitch circles of contact of the meshing teeth have the same diameter, the volume of working fluid (e.g. oil), which is enclosed by the gears and drawn in or discharged, as the case may be, through connecting passages 18, 20, remains constant. In this control position, the gear pump merely constitutes a barrier to the passage of the working medium. However, as soon as the rocker member 8 is pivoted out of the neutral center or zero position by a movement of the control lever 12, for example in the clockwise direction as viewed in FIG. 1, all the gears in the train acquire unequal respective pitch circle diameters of the circle of contact in the two meshing positions needed for discharge, and this takes place in a degree which increases with the angle of pivot. The resulting direction of discharge is always determined by the direction of rotation of the gears and at the same time by the direction in which the rocker member 8 is pivoted.

In order to seal off the cavity enclosed by the gears from the remaining space 19 within the housing 1 in a reliable and satisfactory manner, there must be a fluid-tight fit between the gears and the wall of the housing, on the one hand, and the gears and the rocker member 8, on the other. Depending on the direction of flow, this fit is steadily maintained by the instantaneous prevailing working pressure acting either on the part of the rocker member 8 lying outside the piston-like extension 8' or on the piston-like extension 8' of the rocker member 8 itself in such a way that, if the proportions are correct, the hydraulic forces tending to lift the rocker member are so exceeded by the applied hydrostatic forces that the film of lubricant on the frontal surfaces of the gears is kept precisely at the minimum thickness required. The axial thrust exerted on the gears by the rocker member 8 is also applied to the opposite frontal surfaces, since the gears can be displaced axially on their bearings.

Of course, the principle of using a cover plate, loaded hydrostatically by the working pressure (i.e. the difference between the pressures of the medium at the inlet to and outlet from the pump), to seal the cavity enclosed within the gear train, is not restricted to the embodiment above described. For example, to obtain a certain axial adjustability in the drive shaft 3, or to be able to dispense with the need for superior antifriction properties in the material of the housing, the rocker member 8 can equally well be arranged on both sides of the gears, so that its freedom of axial movement is extended to the entire set of gears in the train or so that the entire set of gears can be aligned axially with the driven gear. Similarly, it is not absolutely necessary that the rocker member 8 should be controlled and actuated by just one piston-like extension 8'. Several hydraulic pistons of this type may be used in addition to or even instead of the extension 8', but distributed over the entire surface of the rocker member 8. The principle of the invention is not at all restricted to a radially displaceable arrangement employing a rocker. For example, the radial displacement of the gears necessary for the continuous adjustment and control of the pump output can also be achieved by mounting the said gears on eccentric shafts, themselves mounted rotatably in housing 1. Eccentric shafts of this type are illustrated in my copending application, Serial No. 77,249, filed December 20, 1960, now issued as Patent No. 3,067,691.

FIG. 4 shows in schematic form another embodiment of the gear pump made in accordance with the principle of the invention. Since the more important components bear the same numbers as the corresponding parts in the example illustrated in FIGS. 1-3, it will suffice, without any further special explanation, to point out that in this embodiment the gear train consists of six gears, while the rocker member 8 in FIG. 4 has simply to be fitted with three bearing pins instead of two as in FIGS. 1-3. The dash-dot lines indicate the range 5 through which the rocker member pivots.

FIG. 5 shows, again in schematic form, another embodiment of the invention. Here the gear pump has the gear arrangement of a planetary gear system, the sun wheel 22 of which, turned by the drive shaft 3, engages planet wheels 23 and 23, which in turn engage the internally toothed rim gear 24. The drive shaft 3 and the toothed rim gear 24 are mounted in respective fixed positions inside a housing 1, whereas the teeth of the planet wheels 23 and 23 and the mounting of the latter within the housing 1 are so designed that the gears 23, 23' are free to move radially. Altogether, there are four four-wheel gear trains and four corresponding pump chambers enclosed only by the gear wheels and two ring-shaped cover plates (not shown), each chamber being capable of functioning separately. As long as the centers of planet wheels 23 and 23' all lie on the same circle C (FIG. 4), all the displacement eifects are neutralized and the pump merely acts as a barrier to flow. However, as soon as the centers of the two gea-r pairs 23 and 23', each pair being formed by respective diametrically opposite gear wheels, are at ditferent distances from the center axis of the sun wheel 22, there are formed, for example, cavities A with an increasing amount of working medium and cavities B with a decreasing amount of working medium. The output of the pump depends on the difference 6 (FIG. 5) between the center-to-center distances; the direction of flow depends both on the direction of rotation of the sun wheel "and on which of the above-mentioned two gear pairs 23, 23 has the greater center-to-center distance.

It will be immediately clear from the foregoing that, here, as in the other embodiments, without detriment to the operating principle of the pump, the two gear pairs 23, 23' can be mounted in the housing (not shown in FIG. 5) so as to be capable of continuous radial adjustment, for example by means of eccentrics, of the type shown in the above-mentioned copending application, Serial No. 77,249, etc., and that such pump will also then be both reversible and smoothly adjustable in both directions of flow. Likewise, it requires no further explanation that in this instance likewise the pump chambers can be laterally closed by means of hydrostatically loaded, axially movable cover plates. Finally, it is also worth mentioning that, as in the examples shown in FIGS. 1-4, the number of gears per chamber or gear train in FIG. 5 may exceed the minimum of four and may be equal to any number divisible by two. Furthermore, in an arrangement in accordance with FIG. 5, there can be at least two or any greater number of planet wheels 23, 23'.

It will be obvious to those skilled in the art, upon studying this disclosure, that devices according to my invention can be modified in various respects and hence may be embodiend in apparatus other than particularly illustrated and described herein, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

I claim:

1. A hydraulic machine comprising a housing having inlet and outlet ducts for hydraulic medium, a closed train of gears comprising at least four gears defining a path through which said medium passes, means rotatably mounting at least one of said gears in said housing in radially fixed position, and means mounting another of said gears for variable displacement of said other gear in a direction transverse to the rotational axis thereof so as to vary the specific delivery quantity and direction of said medium passing through said gear train, at least each alternate gear in said gear train being variably displaceable in a direction transverse to the rotational axis thereof, each two adjacent mating gears of said train defining together two instantaneous circles of contact of variable diameters corresponding to variable depths of engagement of the meshing gear teeth thereof, and means for guiding the displaceable gears in said housing and for adjustably varying the size of said diameters in respectively opposite senses to a predetermined value so that radial displacement of a displaceable gear of said train in one direction results in a variation in an opposite direction of the depth of engagement of the teeth of the gear mating therewith.

2. A hydraulic machine comprising a housing having inlet and outlet ducts for hydraulic medium, a closed train of gears comprising at least four gears defining a path through which said medium passes, means rotatably mounting at least one of said gears in said housing in radially fixed position, and means mounting another of said gears for variable displacement of said other gear in a direction transverse to the rotational axis thereof so as to vary the specific delivery quantity and direction of said medium passing through said gear train, each gear of said gear train being provided with sealing means on its frontal surface, and means defining a clearance space between the outer peripheries of said gears at the tooth heads thereof and the adjacent port-ions of said housing which is substantially greater than normal running clearance.

3. A hydraulic machine comprising a housing having inlet and outlet ducts for hydraulic medium, a closed train of gears comprising at least four gears defining a path through which said medium passes, means rotatably mounting at least one of said gears in said housing in radially fixed position, and means mounting another of said gears for variable displacement of said other gear in a direction transverse to the rotational axis thereof so as to vary the specific delivery quantity and direction of said medium passing through said gear train, said housing having a central shaft journalled therein, the radially fixed as well as the displaceable gears of said gear train being together arranged concentrically around said shaft, said means mounting said other gear including a rocker member pivotally mounted in said housing and provided with bearing pin means rotatably supporting said displaceable gears, and means for swingably rocking said rocker member about said shaft.

4. Hydraulic machine according to claim 2, said gears of said gear train including a sun gear having a fixed axis of rotation, a plurality of planetary gears in engagement with said sun gear, and an internally toothed rim gear fixedly mounted in said housing and in meshing contact with said planetary gears, and means mounting said planetary gears in said housing so that said planetary gears are radially displaceable.

5. Hydraulic machine according to claim 2, said gears of said closed gear train comprising bevel gears.

6. A hydraulic machine comprising a housing having inlet and outlet ducts for hydraulic medium, a closed train of gears comprising at least four gears defining a path through which said medium passes, means rotatably mounting at least one of said gears in said housing in radially fixed position, and means mounting another of said gears for variable displacement of said other gear in a direction transverse to the rotational axis thereof so as to vary the specific delivery quantity and direction of said medium passing through said gear train, said closed gear train defining an inner space enclosed by the gear train, said housing defining an inner cavity around the gear train, axially movable sealing means disposed within the housing and having an outer periphery spaced from the inner surface of said housing, said sealing means being engageable With a respective frontal surface of each of said gears of the gear train for forcing said gears axially against an adjacent housing Wall so as to effect a sealing of the opposed frontal surfaces of each of said gears against the housing and againstsaid sealing means, respectively, to thereby effect a hydraulic separation between said inner space enclosed by said closed gear train and the cavity defined by said housing and around said gear train.

7. Hydraulic machine according to claim 6, said housing having a stationary connecting passage for flow of said hydraulic medium, said sealing means comprising a rocker member having a piston-like extension, said housing having a central cylindrical recess receiving said piston-like extension and providing a radially fixed but axially movable pivoted mounting for said rocker member within said housing, a control shaft centrally mounted in said housing, said rocking member being axially aligned with said control shaft and drivingly connected thereto, said rocker member including walls having outer surfaces sealingly engageable with the frontal faces of said gears and defining an inner bore communicating with said stationary connecting passage.

8. Hydraulic machine according to claim 6, said housing having a control shaft journalled therein, said sealing means including a rocker member pivotally mounted in said housing concentric with said control shaft, said rocker member having internal gearing drivingly connecting same to said control shaft so as to provide an axially movable but rotatably fixed driving connection between said control shaft and said rocker member, said means mounting said other gear forming part of said sealing means and including bearing pin means rotatably supporting said displaceable gears of said gear train.

9. Hydraulic machine according to claim 6, said sealing means comprising rocker members arranged on both opposed frontal sides of said gears of said gear train, means mounting said rocker members for axial and rotatable guidance within said housing, said housing having a stationary connecting passage for fiow of said hydraulic medium, and means in said housing providing a space communicating with said stationary passage for flow of hydraulic medium against said rocker members to provide delivery hydraulic pressure to press said rocker members toward each other, one of said gears of said train being a driven gear and having a drive shaft, the other of said gears being axially adjustable relative to said driven gear.

References Cited by the Examiner UNITED STATES PATENTS 2,371,227 3/1945 Dodge 103-126 2,549,241 4/1951 Rorive 103120 2,765,749 10/1956 Mosbacher 103126 2,948,228 8/1960 Ahlen l03-120 FOREIGN PATENTS 599,654 3/1948 Great Britain.

KARL J. ALBRECHT, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner. 

1. A HYDRAULIC MACHINE COMPRISING A HOUSING HAVING INLET AND OUTLET DUCTS FOR HYDRAULIC MEDIUM, A CLOSED TRAIN OF GEARS COMPRISING AT LEAST FOUR GEARS DEFINING A PATH THROUGH WHICH SAID MEDIUM PASSES, MEANS ROTATABLY MOUNTING AT LEAST ONE OF SAID GEARS IN SAID HOUSING IN RADIALLY FIXED POSITION, AND MEANS MOUNTING ANOTHER OF SAID GEARS FOR VARIABLE DISPLACEMENT OF SID OTHER GEAR IN A DIRECTION TRANSVERSE TO THE ROTATIONAL AXIS THEREOF SO AS TO VARY THE SPECIFIC DELIVERY QUANTITY AND DIRECTION OF SAID MEDIUM PASSING THROUGH SAID GEAR TRAIN, AT LEAST EACH ALTERNATE GEAR IN SAID GEAR TRAIN BEING VARIABLY DISPLACEABLE IN A DIRECTION TRANSVERSE TO THE ROTATIONAL AXIS THEREOF, EACH TWO ADJACENT MATING GEARS FO SAID TRAIN DEFINING TOGETHER TWO INSTANTANEOUS CIRCLES OF CONTACT OF VARIABLE DIAMETERS CORRESPONDING TO VARIABLE DEPTHS OF ENGAGEMENT OF THE MESHING GEAR TEETH THEREOF, AND MEANS FOR GUIDING THE DISPLACEABLE GEARS IN SAID HOUSING AND FOR ADJUSTABLEY VARYING THE SIZE OF SAID DIAMETERS IN RESPECTIVELY OPPOSITE SENSES TO A PREDETERMINED VALUE SO THAT RADIAL DISPLACEMTNT OF A DISPLACEABLE GEAR OF SID TRAIN IN ONE DIRECTION RESULTS IN A VARATION IN AN OPPOSITE DIRECTION OF THE DEPTH OF ENGAGEMENT OF THE TEETH OF THE GEAR MATING THEREWITH. 